A self extracting crank is effectively a bolt on top of a bolt (often with an opposite thread). So you undo the inner bolt, it hits the outer bolt, it can’t move, so pulls the cranks off from the axle. If this self extractor nut rattles loose and falls out it makes removing your cranks a lot harder than it needs to be or you’ll have to buy a new crank bolt kit…. Usually at a fairly high price for what it is.
I come across this quite regularly when servicing bikes, especially on SRAM DUB cranksets, so I thought I would give you some advice as to how to prevent it happening to you. More often than not I just find them loose but still in the crank but worth checking yours!
The next time you are giving your bike a check over or having a mechanic service it, ask them to check this bolt and apply some more loctite if it’s loose. It is a very simple task as you can see and might save you a headache later.
You will usually need a pin spanner or a 10 - 12mm Allen key to tighten the bolt and it will often be an opposite thread. apply a bit of pressure If yours is tight probably best to leave it be but keep an eye on it regularly.
How to maintain tighten and reapply lactate to a self extracting SRAM DUB crank bolt.